ARTICLE IN BRIEF
While stroke death rates in the US have declined in 40 years, a new analysis by the Centers for Disease Control and Prevention show that the rates have plateaued slightly in the last few years. Stroke experts and epidemiologists offer an analysis of what that might be so.
After a considerable decline spanning more than four decades, the rate of US stroke deaths has abated in recent years for reasons that remain unclear, a new report from the US Centers for Disease Control and Prevention (CDC) revealed.
Among U.S. adults aged 35 years or older, age-standardized stroke death rates dropped 38 percent, from 118.4 per 100,000 persons in 2000 to 73.3 per 100,000 persons in 2015. However, from 2013 to 2015, there was a 2.5 percent increase in stroke death rates per year, according to the September 8 Morbidity and Mortality Weekly Report.
Although improvements in modifiable stroke risk factors and in stroke treatment and care over time led to the prominent decline in stroke death rates, the report did not directly conclude what caused the slowing, stalling, and reversing of patterns.
“This study focused on describing the trends” and not on investigating the contributing causes, said Quanhe Yang, PhD, the report's lead author and a senior scientist with the Epidemiology and Surveillance Branch at the CDC's Division for Heart Disease and Stroke Prevention, told Neurology Today.
More than likely, “multiple factors contributed to this significant reversal or stalled progress, including the effects of a long-term epidemic of obesity and diabetes in the United States,” Dr. Yang explained. “Stalled progress in stroke death rates accompanied by an increase in obesity and diabetes is of considerable concern. Younger generations are living with obesity and diabetes for a longer period of time, which will likely present new challenges for preventing stroke deaths in the future.”
Obesity is a major cause of hypertension, the single most important modifiable risk factor for stroke. Despite recent strides, nearly half of the 75 million U.S. adults with hypertension have uncontrolled blood pressure, according to the report. The authors suspected that changes in some other stroke risk factors — such as diets high in sodium and added sugar as well as smoking, physical inactivity, and unhealthy weight — over the past few decades may be contributing to the slowing of the decline.
About 80 percent of strokes are preventable. Nonetheless, among younger adults (18 to 64 years of age), researchers observed a significant increase in both stroke hospitalizations and in related stroke risk factors — hypertension, obesity, diabetes, lipid disorder, and tobacco use — documented at the time of the acute stroke hospitalization from 2000 to 2012.
The authors predicted that “these changes in modifiable stroke risk factors might present new challenges for stroke prevention and for maintaining a sustained decline in stroke mortality in the United States.”
They also noted that the patterns in stroke death rates could be associated with adverse changes in the prevalence or management of risk factors, which may increase stroke incidence and other time-limited factors, such as complications of a severe influenza season, such as with drifted H3N2 influenza in 2014 to 2015.
STUDY DESIGN, RESULTS
The CDC examined trends and patterns in recent stroke death rates by age, sex, race/ethnicity, state, and census region. The National Vital Statistics System provided data for the analysis of stroke death rates as the underlying cause of death from 2000 to 2015. Researchers conducted trend analyses based on the age-standardized or age-specific stroke death rates.
In the two years leading up to 2015, the last trend segment indicated a reversal from a decrease to a statistically significant increase in stroke death rates among Hispanics, with an annual percent change of 5.8 percent, and among persons in the South Census Region an annual percent change of 4.2 percent.
Furthermore, in 38 states (75 percent), declines in stroke death rates were not sustained. From 2013 to 2015, an estimated 32,593 excess stroke deaths might not have occurred if the prior rate of decline had continued.
The list of states included eight of nine in the Northeast Census Region, seven of 12 in the Midwest, 14 of 17 in the South, and nine of 13 in the West. In Florida, the decline in the stroke death rate reversed during 2013 to 2015, with a significant increase (10.8 percent per year) in the stroke death rate.
“The findings of this study will help identify populations that could benefit from interventions to prevent and control modifiable stroke risk factors, further improve the quality of care, and reduce stroke prevalence and mortality,” the authors wrote.
Several neurologists interviewed by Neurology Today commended the researchers for calling more attention to factors that play a major role in stroke mortality, while stressing far more vigilance to overcome the recent plateau in stroke death rates.
The CDC data offers the most comprehensive way to examine stroke mortality, but the number of deaths captures only part of the story, said Dawn O. Kleindorfer, MD, professor of neurology and director of the vascular neurology division at the University of Cincinnati.
“Whether people are dying from stroke doesn't tell you whether fewer strokes are happening or if they're dying less after they have them. Did we get better at treating them after they occurred?” Dr. Kleindorfer asked. “It's an outcome that's a little bit difficult to interpret.”
Delving deeply into the issues contributing to stroke death rates would help uncover an important piece of the puzzle. For instance, a decade ago, researchers demonstrated that more African-Americans were dying of strokes than whites because the incidence of stroke was higher in blacks than in whites, she said. The new report confirmed this trend.
Some of the stroke mortality data could hinge on how hospitals document the causes of death of patients with co-morbidities, said Stacey Quintero Wolfe, MD, associate professor and residency program director in the department of neurosurgery at Wake Forest University School of Medicine in Winston-Salem, N.C.
“Patients with more co-morbidities have a higher severity of illness, which can be used to create an adjusted mortality,” said Dr. Wolfe, who is also director of neurointerventional surgery. Depending on the tabulations, the findings will show “some degree of a plateau” in stroke death rates.
“But when we're speaking not just about calculations, but taking care of real patients, which is what is really important, we still have some work to do,” she said. “One of the solutions will be ensuring that all patients who are candidates for endovascular therapy receive mechanical thrombectomy to prevent mortality and improve functional outcomes.”
“The timely report from the CDC may signal a wakeup call to renew the vigor to make stroke prevention more of a priority,” said Daniel T. Lackland, DrPh, FACE, FAHA, FASH, professor of translational neuroscience and population studies in the department of neurology at the Medical University of South Carolina in Charleston.
In trying to make sense of the plateau, he speculated that clinicians may have become complacent about pushing for stronger blood pressure control and ensuring that patients were adhering to their therapies. “We may have become a little more complacent and casual about that, and maybe it's time to re-energize that and emphasize it with the same kind of passion that we did previously.”
Dr. Kleindorfer said the formidable challenge lies in convincing patients to become more actively engaged in preventive strategies. Medicines may be too costly and the side effects so unpleasant that some patients could decide to skip doses or forgo taking them altogether, leading to devastating consequences.
“A lot of my patients have trouble understanding why they need to worry about their blood pressure and their blood sugar when they feel fine,” she said. “They don't feel badly until they have a heart or a stroke.”
Dr. Kleindorfer added that neurologists “can't be complacent” simply because stroke now ranks lower on the list of serious health conditions most likely to take lives. According to the CDC report, stroke death rates in the United States have declined since at least the 1960s, falling from the third to the fourth leading cause of death in 2008 and to the fifth in 2013. Age-standardized rates among adults aged 35 years or older declined from 315.7 deaths per 100,000 in 1968 to 73.3 per 100,000 in 2015.
Nearly 800,000 individuals in the United States still suffer a new or recurrent stroke each year, and about 140,000 stroke victims die. As a result, stroke accounts for one in every 20 deaths and is also a leading cause of serious long-term disability, with an estimated annual cost of $33.9 billion, according to the CDC report.
The authors acknowledged that the report's findings have at least a half-dozen limitations. Death certificates may list a misclassified underlying cause of death, and age-standardized stroke death rates do not represent actual stroke death rates, which will vary more from the unadjusted rate as the population distribution changes over time. To address this concern, age-specific rates were also computed.
Furthermore, researchers estimated excess stroke deaths by assuming they would continue to decline through 2015 at the annual rate of the most recent APC, and so this represents the hypothetical achievable reduction in stroke deaths.
As the decline in stroke death rates has leveled, “we must be vigilant about trying to find new ways to prevent stroke from happening,” Dr. Kleindorfer said. “Treating it afterwards is important for sure, but I believe we should be trying to prevent stroke more than we are right now.”
EXPERTS: ON THE PLATEAU IN STROKE DEATH RATES